1. Field of the Invention
The present invention relates to a resin composition and a laminated product using such resin composition. More particularly, this invention is concerned with a fire-retarding or uninflammable resin composition obtained by mixing a specific inorganic filler into a polyolefin resin, and a laminated product composed of metal sheets or foils and such fire-retarding resin composition in sheet form interposed between the metal sheets.
2. Description of the Prior Art
Various kinds of material, when they are used, in general, as a building or constructional material, and so forth, are always desired to have higher uninflammability or fire-retarding property, because the higher the uninflammability or fire-retarding property thereof is, the wider will be their utility.
For instance, a laminated product of a metal-synthetic resin-metal structure obtained by interposing a synthetic resin sheet between a pair of metal sheets in a laminal structure possesses various features such that it is of light weight in its entirety, which is closer to that of the synthetic resin per se, and has the mechanical properties such as bendability, etc. and the heat-resistant property as well much superior to those of a product made simply of the resin composition to be used as the core material for the laminated product. In view of the fact that the synthetic resin sheet is covered on its both surfaces with the metal material, the laminated product has its considerably favorable fire-retarding property in comparison with the product made of such synthetic resin material alone. It has, however, been found out through the past experience in the practical use of such laminated product that, since the resin as the core material is usually exposed at the lateral end faces of the laminated product, the resin material catches on fire when the laminated product is exposed to flame, and the molten resin drips to cause fire to expand or spread. In order to remove such defect of an accidental nature, it is necessary that the resin to be the core material for the laminated product be vested with uninflammability or fire-retarding property.
For rendering the resin to be uninflammable or fire-retarding, there has so far been taken a measures such that a large amount of inorganic filling agent is mixed into a resin material such as polyolefin resins, etc. to thereby decrease its heat-generating quantity and, at the same time, to suppress production of black smoke so as to prevent molten resin from dripping.
As the inorganic filling agent to be mixed with the resin material for giving it the desired fire-retarding property, there have been known those inorganic fillers such as calcium carbonate, magnesium oxide, magnesium carbonate, calcium silicate, aluminum silicate, talc, and so forth; and inorganic hydrates containing therein crystal water such as aluminum hydroxide, magnesium hydroxide, and so on.
However, for the purpose of mixing, calcium carbonate, magnesium oxide, calcium silicate, talc, and other inorganic filling agents are required in an extremely large quantity, and no satisfactory result can be obtained practically unless it is in a quantity of 400 parts by weight or more with respect to 100 parts by weight of polyolefin resin. On the other hand, magnesium hydroxide, aluminum hydroxide, and other inorganic hydrates possess, to a certain extent, their effect of decreasing their heat-generating quantity and preventing the molten resin material from dripping, because such substance has the endothermic effect at the time of their decomposition by dehydration from heat of combustion. However, even these inorganic hydrates are unable to prevent the molten resin from dripping, unless they are mixed in an extremely large quantity such as, for example, as large as 300 parts by weight with respect to 100 parts by weight of polyolefin resin, when the resin material is required to have high uninflammability or fire-retarding property for those circumstances such as fire where the resin material should be subjected to high temperature flame, hence no satisfactory effect can also be obtained from such inorganic hydrates.
Such resin composition which requires a large amount of inorganic filling agent to be mixed thereinto becomes very difficult to be pelletized, hence it is unable to meet the practical purpose; and, when it is processed into a shaped product, it brings about decreased fluidity within the extruder or dies to make it difficult to be formed into an appropriate shaped product. Furthermore, the shaped product is liable to be brittle owing to loss of pliability which the polyolefin resin possesses, to increase its specific gravity, and other unfavorable effects.
When this resin is used in the afore-mentioned metal-resin-metal type laminated product, the uninflammability of the laminated product improves; however, there would inevitably brought about new disadvantages such that its bending property becomes considerably deteriorated with consequent breakage of the metal plates covering the surface of the core resin when the laminated product is subjected to bending. In addition, since the resin material has high specific gravity, the light weight property (the property specific to the laminated product) would be lost.
As the results of studies and researches done by the present inventors as to the cause for insufficient prevention of the molton resin material from dripping by those inorganic hydrates containing therein crystal water such as aluminum hydroxide and magnesium hydroxide, out of various inorganic fillers, which surely bring about decrease in heat of combustion and exhibit a certain degree of effect toward uninflammability of the resin, it has been found out that, as the first cause, the decomposition by dehydration of the crystal water takes place in a narrow range of temperature, that is to say, the decomposition by dehydration abruptly occurs in a temperature range of from 200.degree. C. to 300.degree. C. for aluminum hydroxide and in a temperature range of from 300.degree. C. to 400.degree. C. for magnesium hydroxide, which causes foaming by the water content to deprive the resin composition of its self-sustaining property, and, as the second cause, the filling agent is in a simple granular form which can not afford to bring about entanglement among such granules, hence such shape is not effective for prevention of the molten resin from dripping.